Vehicle tire inflation systems are typically installed in trucks and truck trailers to deliver pressurized air to tires and maintain air pressure at a safe level during operation. Typically, these tire inflation systems are employed on truck trailers which do not have the drive axles. This is because pressurized air can be easily routed either within or along the non-rotating trailer axle and delivered to the rotating tires, such as via a rotary union. Examples of some trailer axle tire inflation systems invented by the applicant of the present invention can be seen in U.S. Pat. Nos. 5,287,906, 5,377,736, and 6,425,427, the teachings of which are incorporated herein by reference.
The industry has accepted inflation technology for trailers, which technology uses the axle beam as a conduit for air delivery, whether the axle itself is pressurized and conducts air, or a separate, internal air line extending therealong is used. This method of air delivery is optimal as it keeps external plumbing in critical areas to a minimum, and it delivers air to the center of the wheel hub base or hubcap for delivery to the respective tires.
Currently, there is no known drive axle technology that utilizes the drive axle shaft itself as an air conduit, primarily because the drive axle is a solid shaft and it rotates within a differential housing with very little clearance between the shaft and housing wall. One solution is known that provides an air line between the rotating axle shaft and the housing wall and which terminates off center and outside the wheel hub face. This approach is not only impractical and short-lived due to complications inherent in running an air line through that passage, but it also ends up supplying air at an off-center (non-optimum) point outside the axle and substantially removed from the very center of the wheel hub face or hubcap.
Further complicating the drive axle system is the fact that drive axles typically employ splines disposed about the drive axle, and which splines typically have an outer diameter (OD) that is greater than the drive axle. These drive axle splines and relative dimensioning complicate the delivery of pressurized air to a wheel end and tires via the drive axle. There is desired a drive axle tire inflation system configured for use in medium and heavy duty vehicles, with minimum plumbing, whereby an air source can be delivered to tires in a reliable and cost effective manner.